1. Field of the Invention
The present invention generally relates to a digital oscilloscope using a color plane display device and to a data display method in such a digital oscilloscope. More specifically, the present invention is directed to a digital oscilloscope using a color dot matrix plane display device and also to a data display method performed in such a digital oscilloscope.
2. Description of the Related Art
Oscilloscopes have been widely utilized to observe waveforms, and therefore are very useful in research/development, production, maintenance, and repair works. As is well known in this technical field, a cathode-ray tube (CRT) has been conventionally employed as the display device of an oscilloscope.
For instance, such conventional oscilloscopes have been proposed in which the color CRT is employed, or the color LCD shutter is provided in front on the CRT (see JP-A-53-84789, JP-A-54-8566, JP-U-58-14171). When such oscilloscopes are employed, the waveforms can be displayed with different color representations in the respective display channels, which can provide very easy waveform observations.
However, generally speaking, cathode-ray tubes necessarily require relatively long lengths from screen surfaces up to electron guns, as compared with the screen sizes. Accordingly this fact prevents compact arrangements of the conventional oscilloscopes.
On the other hand, compact/light weight digital oscilloscopes have been proposed to utilize the liquid crystal displays (LCD). These conventional digital oscilloscopes use monochromatic LCDs. For instance, JP-A-4-143664 discloses such a digital oscilloscope which uses the active matrix type LCD as the display device. This prior art proposes that the switch elements for driving the pixel electrode group are fabricated by way of the silicon single crystal thin-film layer in the device, and such an LCD which is usable in the oscilloscope is thus manufactured.
As previously explained, the color representation of signal waveforms cannot be apparently realized by employing the monochromatic LCD exclusively utilized in the oscilloscope. To perform a color representation of waveform data, either an LCD for a computer display screen (so-called "office automation type LCD") is employed, or a so-termed audio/visual type color dot matrix type plane display device is employed. However, although in the office automation type LCD, a designation of color can be made in correspondence with the waveform display position, there are many drawbacks. That is, since one pixel is accessed by 3 dots (R, G, B), the required resolution in the horizontal direction would be deteriorated when the display screen becomes small. When the size of one dot is made small, higher machining precision is required. Moreover, such a high precision LCD has a high cost, and the resultant oscilloscope cannot be made compact. On the other hand, when the audio/visual active matrix type LCD is employed in the digital oscilloscope, the display control is carried out for every one line, namely, based upon the horizontal sync signal. As a result, such a phenomenon happens to occur in that one pixel of this active matrix type LCD is emitted at a certain position, whereas two pixels thereof are emitted in response to certain display data, resulting in deterioration of the display quality along the horizontal direction.
In particular, when a compact color dot matrix type display device is used in an oscilloscope, since a total pixel number along the horizontal direction is small, a representation quality such as smoothness of a display wave is lowered.
It should be understood that an office automation type color dot matrix plane display device is such a display device that in response to a clock (namely, external clock) derived from a display control unit for controlling this display device and image pixel data synchronized with this external clock, the driving/scanning operations of the pixels are controlled. Also, an audio/visual type color dot matrix plane display device is such a display device that a frequency synthesizer (e.g., PLL) is provided, and the sampling/scanning operations of the externally supplied video signal are carried out in response to the clock produced by the synthesizer.
In the LCD, it is known, as described in JP-A-55-8161 and JP-A-4-314094, that the analog video signal is coincident with the display timing for the audio/visual type LCD. If such a known technique is utilized, then the sampling operation, the signal acquisition at the display device, and the scanning operation can be performed in a stable condition with respect to the sync signal.
As is well known in the art, for instance in a color dot matrix display device, a plurality of pixels of three primary colors, red (R), green (G), blue (B) are arranged in a manner as shown in FIG. 22, or FIG. 23, and these R, G, B pixels are emitted in response to data. FIG. 22 and FIG. 23 are enlarged views of a portion of the pixels in the color dot matrix devices.
Referring now to FIG. 22 and FIG. 23, a description is given for an example of a display method when the color dot matrix display device is used in the oscilloscope to display the data.
It should be noted that symbols X1, X2, X3, . . . , shown in FIG. 22 and FIG. 23 represent coordinate points along the X-coordinate axis (namely, the coordinate axis along the horizontal scanning direction), and then the display data are produced coinciding with this coordinate point. That is, one set of R, G, B constitutes one coordinate point.
As illustrated in FIG. 22, when a plurality of R, G, B pixel arrays are arranged on the line LH along the respective horizontal scanning direction in the order of R, G, B, R, G, B in the color dot matrix display device, assuming now that the first pixel groups in the respective lines are R.sub.1, G.sub.1, B.sub.1, and the second pixel groups in the respective lines are R.sub.2, G.sub.2, B.sub.2, and so on, these pixel arrays are emitted for every 1 line. In other words, the dots R, G, B belonging to each pixel group are emitted in such a manner that the first pixel group R.sub.1, G.sub.1, B.sub.1 in the line LHn is emitted by the first applied data, the second pixel group R.sub.2, G.sub.2, B.sub.2 in the line LH.sub.n+2 is emitted by the second applied data, and the third pixel groups R.sub.3, G.sub.3, B.sub.3 in the line LH.sub.n+4 is emitted by the third applied data.
In this case, the horizontal resolution is equal to the horizontal resolution as indicated by the X coordinates X1, X2, X3, . . . of FIG. 22, since emission of 1 group of the dots R, G, B is carried out in units of resolution.
Also, as shown in FIG. 23, when the R, G, B dot arrangement of the color dot matrix display device is in a delta arrangement, and the dots G, R, B, G, R, B are arranged in the line LHn and the line LH (n+even number) along the horizontal direction, and the dots B, G, R, B, G, R are arranged in the line LH (n+odd number), assuming now that the first and second pixel groups in the line LHn and the line LH (n+even number) are G.sub.1, R.sub.1, B.sub.1, and G.sub.2, R.sub.2, B.sub.2, and so on; and the first pixel group in the line LH (n+odd number) is B.sub.1, G.sub.1, R.sub.1, . . . and the second pixel group thereof is B.sub.2, G.sub.2, R.sub.2, . . . for instance, the dots G and R are emitted (it becomes yellow light). Observing a case in which a horizontal line is emitted on the line LHn, the first pixel group of G.sub.1, R.sub.1 is emitted at the first data (coordinate X1), and the second data is not emitted since there is no same group of dots at the coordinate Xz, and further the second pixel group of G.sub.2, R.sub.2 at the second data (coordinate X3) is emitted. Similarly, the fourth data is not emitted because there is no same group in the coordinate X4. At the fifth data (coordinate X5), the third pixel group of G.sub.3, R.sub.3 is emitted. In this manner, the dots R and G belonging to the respective pixel groups of the respective lines are emitted. However, in this case, since the dots R and G of the respective pixel groups in the line LH (n+odd number) are not present on the same coordinate as the line LHn and the line LH (n+even number), the line LH (n+odd number) cannot be emitted.
Consequently, the horizontal resolution in this case is equal to that indicated by the coordinate points X1, X2, X3, . . . on the X coordinate shown in FIG. 23. As described above, the total number of pixel groups is only half of the total quantity of coordinates, so that the data cannot be effectively displayed.